Correct me if I am wrong but all pre Ts had water pumps and the Model As after. Could the no water pump on the T been the attempt by Mr. Ford to save money???

I found out the hard and expensive way that trying to make an old radiator work isn’t worth it, just get a new one and then see if you want a water pump. I do run water pumps on my Ts simply because I like to go to parades and I think it helps. I have also heard it will rob horse power, if so not enough to notice, I can keep up to every one with my heavy Town Car. Just ask Jim Eck . (HA…HA..) sorry Jim.

There are 3 reasons I don't put a water pump on my car. 1. I would have to buy a new fan belt. 2. I would have to rebuild my fan hub to take the extra load. 3. I would have to replace the 60+ year old radiator hoses

I have always run a water pump with no problem on several T's that I have own. I just finish a 27 Roadster with a new engine and tranny. Clean block and radiator. I am going to run this T with NO waterpump to see how the other lived. My buddy has run no water pump for 30 years with no trouble. So here goes. There nothing like a T in my book.Best car Ford ever built.

My '23 touring seems to do OK without one. The old saying, "If it ain't broke, don't fix it," seems to apply here. If the car works without it, why complicate things by adding more moving parts that can go wrong?

Someone recently posted the density change of water with temperature on the forum. It turns out that there is very little density change until the water gets really hot, near the boiling point. This means that a thermosiphon system will naturally run hot without a themostat.

Engines should be run hot (near the boiling point of water). The reason is that the gasoline is more thoroughly vaporized and the water vapor, a product of combustion, is not condensed to form acid in the crankcase. Gasoline has to be in a vapor form to combust efficiently.

An engine that has a water pump installed will run cooler, and perhaps too cool, unless it also has a thermostat installed. I always ran a thermostat at the discharge neck of my Model A's.

I suspect that Mr. Ford removed the water pump for two reasons: reliability and cost. The later Model A pumps always leaked a little and had to be rebuilt from time to time. It is likely the pre T and first T water pumps were not reliable.

The problem with water pumps on a Model T is that they are a major source of breakdowns, yet do not add any improvement in performance. You can debate all you want, but the fact will remain that water pumps stop more Model T's on tour than any other single item. If they are not leaking then the shaft is seized up. When the shaft seizes up then the engine overheats. When all the water leaks out the car overheats. Either way, the owner of a water pump equipped Model T gets lots of attention.

The reason that the T runs as warm as it does on a warm day is called "delta T". It has to run warm on a warm day because it has to get hotter than the ambient temperature by a certain amount to reject the heat.

Which is also why it runs too cold on a cold day - unless it has either a thermostat or a winter front on the radiator.

That line looks pretty linear to me. It says thermobarf is going to circulate constantly, regardless of temperature in the head.

If you figure out a way to make your engine sluff off more heat on cool days, and less on hot days, then you can keep the head temp in control without a thermostat.

You have an up to 1700 degree fire in the chamber, surrounded by aluminum alloy pistons that melt at 1100 degrees, oil in the block that boils at 250 F, and coolant just beyond the walls that boils at 212 or less. It's a collection of compromises. Too little cooling, and failures follow. Too much cooling, and the fire is quenched, requiring richer mixture and all its effects, such as plug fouling. . The best you can do is provide a constant temperature of the coolant, and enough oil.

You will indeed receive a tongue lashing for distributors, 12 volt conversions and possibly alternators. The rest, probably not. You're more likely to get a tongue lashing for something that shows than you are for something that doesn't.

While I usually practice more tact than some, I probably feel the same way as those who don't. To me....and this is just me.....You do what you want with your own car......Of those things, the alternator is the worst, in my opinion, because it is just plain ugly and out of place under the hood. Water pumps and distributors can be era correct. As for the original question....I wouldn't want a water pump. Why? Because it didn't come with one. I think it is just neat as "L" that the dang thing will work without one! That is one of the things I point out (As I try to educate people on the Model T) to people at car shows. It is one of things I'm inclined to write on windshield placards at a local show under "Intersting Features". I'll put "No water pump, fuel pump or oil pump." Pretty neat, huh? I don't want a water pump for the same reason I don't want a lot of the things on the list. I'm willing to accept the Model T on its own terms and with its limitations. I don't want to just DRIVE the Model T. I want to EXPERIENCE the Model T. Its shortcomings are just part of the experience.

The old story that water will not thermosiphon untill it gets to the boiling point is pure BS Can you honestly tell me that a T driven 50 miles on a cool day with no water pump and stayed about 160 degrees F. did not thermosiphon?

I think if you are tongue lashed for having directional lights it is comming from a guy who does not drive his T much and when he does is a traffic nuisense.

A distributor can keep a T running that has a dead mag system, a 12 volt battery can do the same.

How about the guys that have white or yellow otherwise stock T's? Isn't that worse that a waterpump? Or a stoplight? Or carrying a side-mount spare on a brass car?

I have had good luck with the Texas T water pump. No leaks and the pump turns free. Has been on our T for approx. 5yrs. Because the housing is made of aluminum, you have corrosion to contend with....just like those using Z or other aluminum heads. Most water pumps I have seen on model T's are old, do leak and are prone to binding up. I agree with Royce on old pumps being a source of problems. On the forum, it has been said that most old pumps do not work well....leaving some that do. Having only used a Texas T pump, I have no personal experiance using other make water pumps.

Ford vehicles from model A's on are using water pumps. Modern water pumps are reliable and last many years unless they have a manufacturing defect.

The Texas T pump has a stainless shaft/impeller, modern seals and bearings like those used in pumps produced today. If you have a pump that is reliable, helps keep your T from over heating.....I don't understand why folks get so worked up over others using a water pump. I installed the water pump as last resort to resolve the over heating problem with our T. It's much more enjoyable driving our T with out the constant worry about over heating.

I just hope and pray.....that my water pump never fails.....expecially if on tour with Royce. Smile!

When does anti-freeze coolant start breaking down? I had my high performance 1990 Nissan 300ZX Twin Turbo serviced and the coolant has been in there since February, 2005 and still worked fine (but I had it changed out anyway). Jim Patrick

Jim, I don't know when anti freeze breaks down but for some reason the coolant will go acidic. There are test strips available to check for that. We had a Farmall M that never had the anti freeze acidity checked, just the freeze point. This went on for years until I eventually got drafted. When I finally came home after 4+ years I found the M was down and out. Looking into the problem I found the cast iron BLOCK had corroded around #4 cylinder sleeve allowing the coolant to leak into the oil pan. This engine uses wet sleeves. Now, cast iron is very corrosion resistant, so the coolant had gotten quite corrosive for this to happen. I change coolant every 4 years now, treat the used coolant as a hazardous waste, and properly dispose of it.

I'm somewhat new to Model T's, 2 1/2 years. I've watched the forum for approx 2 years. My truck doesn't have a water pump and does not run hot. I've read the debates about water pumps and never said anything because I didn't feel that passionate about dictating what somone else did with their car. They were a period accessory and if some one needs or wants a water pump, Go for it.

I don't know that a majority of people reject certain accessories. It's just the same ones doing it over and over again, and that draws more attention. The water pump failure picture is always the same picture.

Something Aaron said. puts it all in prospective for me.

Quote "I think if you are tongue lashed for having directional lights it is coming from a guy who does not drive his T much and when he does is a traffic nuisance." close quote.

We all drive under many traffic, climate, and road conditions. It's your car, do what you want, I'm going to.

The thermosiphon system is going to operate like a natural thermostat. That said, a cold day, or running down the road with little load, or having a good radiator, will naturally make the engine run cooler. A themostat and water pump will keep the engine temperature at a constant temperature within tight bounds while the thermosiphon system has wider bounds. Running a water pump without a thermostat will mean that the engine will run cooler, perhaps too cool.

John - I think you should put a water pump on your beautiful TT, even though it doesn't run hot. And, while your at it, even tho' you're probably quite healthy and physically fit, you might as well have a pacemaker installed too, you know, just to be safe,.....ha,ha......harold

(....probably a poor analogy, but that's kinda' my "take" on water pumps on Model T Fords)

Harold, I don't want one. I don't want turn signals, air horns souped-up engines, disc brakes or many other things. As long as I live and drive around out here out here in "Corn Field County", I get along fine. Now if I had to deal with a lot high speed traffic etc., I may want and need all those things, to include a Pacemaker.

My car came with a Teaxs T water pump and took it off and put it against the wall. Now my car dosent spit water all over the floor when I shut it down. Two days ago here in Florida it hit 90 and my car ran nice and cool, even in heavy traffic. But on the other side, When I drive in NY in the cold weather it does run to cold and I need to block off half the rad to get some engine heat

Kenneth, that all happened in the mid 40's. I do recall there was a seal at the base of the sleeve and the engine block had corroded enough that coolant was leaking by that sleeve seal. The block was deemed unrepairable so the engine was swapped out with a used replacement. If it wasn't a wet sleeve I don't recall why the sleeve seal was there. This tractor was acquired immediately after WW II so perhaps later models went to dry sleeves. We also had an H which we souped up with M & W oversize sleeves, this was a very early H, and as I recall the sleeves were wet on that one also. Perhaps my memory is failing like every thing else.

My car came with a water pump therefor I won't remove it, it runs just fine the way it is, I'm in 100% agreement with John Berch where and how much you drive your car will dictate what things you may think will make your car run how you want it, besides it is your car after all.

My TT came with a water pump on it, and I took it off. This past July I ran it in a parade (without the pump) that runs about 6 miles, and the temp on the motometer only reached up into the "summer normal" circle once in that 6 miles. Outside temp was in the upper 80's that day. I'm pretty sure that my radiator is close to original as well.

Rick, to answer your question, you get crusified because the water pump is a mask for other problems and because they do cause break downs. I think everyone has their own ideas of what a T should look, run and drive like. Personally on your list below I only have problems with Distributors, Alternators, 12 Volt Conversions, Turn Signals and Water Pumps.

You left out a couple upgrades I also like, the modern bearing pinion bearings, cut outs that are voltage regulators and fan hubs. All of those help depenability and provide lower maintenance. They also don't change the appearance of the engine or car either. But that's my opinion and I don't care what anyone else thinks.

I put a lot of miles on my T and I want certain low maintenance items on them. I like to have my T's to look and sound like stock T's but maybe pull just a little better due to hills I encounter on some of the tours I attend.

Performance enhancing parts have been around for a long time. Look at how many timers and carburators that have been made as an example. Ruckstell axles were a period accessory that the dealer could sell and install as another example. Water pumps are not performance enhancing, they are band-aids for other issues like excess scale and sediment in the water jackets, plugged radiator tubes etc... I've had John Deere A's that were thermosyphon systems. They were used to bush hog fields among other chores on some very hot humid days and they never got hot. The Thermosiphon systems work, but all the components have to perform their proper function.

I'm wondering if you chose this subject to try and "out do" the "Methanol" post. I don't think that will happen. But any posts regarding oils, band materials, water pumps and others are a sure guarantee to get for getting a number of responses even though all them horses have been beaten to death.

Thermo siphon systems were used well past the era of the T on bigger engines that did much more work. Water pumps didn't really hit it big on tractors until the 60's and that was mainly to help with the loads of bigger hydraulic systems. Essentially, a water pump "over cools" an engine, meaning that it keeps water at a fairly constant temp, whereas the temp at the top of the head could be anywhere from 20-30 degrees warmer than that coming out of the bottom hose where it's cooler.

The system should keep itself in balance with ambient temperatures unless something is offsetting things like fuel mix or insufficient air across the radiator fins, which are good things to blow out every now and then to make sure you have plenty of surface area to cool over.

Clean the radiator. Sounds great on the surface. However, I've determined that the crud on my radiator, while blocking heat transfer, is also sealing the d@mned thing up! Maybe a year ago, I tried cleaning the inside with vinegar. It may be cleaner now, but I liked to have never got it to quit leaking afterward. Still was on the verge of overheating. The other day, I had the novel idea of cleaning the outside. Maybe the crud on the outside is what's keeping it from cooling properly. This is a 'cellular' or honeycomb type, not a tube and fin type. I thought why not take a rifle bore brush and run it through the holes. It cleaned out a lot of dusty crud, but it started leaking. I cleaned out 3 rows and had probably 6 leaks! Glad I started at the top instead of the bottom. Still leaks ocassionally! Boy do I need a new one! But you can bet my money will be spent on a radiator and not a water pump.

When I use to clean out the radiators on some of the diesels we ran I wondered how any air every got through them to begin with. Even though it seemed like it was in good shape, you did well to clean it those holes could have gotten worse over time and left you in a very bad way.

It sort of reminds me of when I'd clean off the differentials on cars and what not. Never leaked a drop of oil while they were caked with mud, but the minute you wipe it all away the flood gates open.

Nope,The M was dry sleves from the word go and on the farm next door there was a M that went through a fire and bought cheap! The pistons were shot so the sleves were removed and the 450 pistons ran in the block no sleves!! Pulled strong but it would heat up when pulled hard! The F-20 had no water pump at first but the later ones did. The B A and G JD's had no water pumps till about 1950 then they all did! Back to T's Anyone who say's all T's have ran cool for the last 100 years with no problems even when new i think is full of ?? Have very many ever ran their T off road in deep sand?? I have,and between the early steering and the small radiator it will make you wonder just how in the heck the old timers did what they did! Put it too work and see what happnes! Bud.PS,How much HP are you using putting along in a parade?? Bud.

Seth, Why would he have built so many with out a pump if he thought they were needed? So what if they would have cost the consumer a couple dollars extra. I'm personally un-impressed with your assumptions of what Henry was thinking or trying. Do you have nothing better to do than keep crap stirred up? The cars and engines must not have been too bad with all that have survived.

Why do suppose Ford had to cover this topic? Read the paragraph starting at the bottom of the left column.

If you didn't want it to boil over on a long hill, you installed a waterpump. There were at least 60, and maybe hundreds of brands for the T.

"Perhaps twisting the fan blades..." Maybe that has caused even more of them to break all these years later.

If you are actually concerned about reliability and safety with your Thermobarf cooled T, you can remove the fanbelt, and save it for parades. I haven't run a fan in years, after learning from Tom Carnegie. I don't do parades, anyhow.

That article brings up a good point, the engine would run at peak efficiency if the water were as close to boiling as possible. That's one of the reasons why it needs to be kept as full as possible so the water wont flash to steam in any air pockets.

I wonder if anyone had ever thought to make a lower pressure cooling system to raise the boiling point to say around 230. It wouldn't take much, modern cars use a 15-20 psi radiator cap, I suspect a T could use one under 5 psi and run fine.

Ricks, maybe they had to cover the article so people could understand the causes of overheating. Maybe people were blaming lack of water pumps then like they do today as the cause rather than identifying the "root" cause of overheating. Cooling systems that boil under ordinary driving conditions are showing a symptom. You chose to ignore the paragraph listing 10 of the root causes in the article. Just because there were 60+ manufacturers of water pump don't mean that they're correct. They're still band aids.

I think people tend to miss the point of the Model T. The Model T was an optimally designed car - for what it was. Yes, there were better designed cars available at the time, but not for $200. Cost was a critical design factor, however reliability was also a factor. Making things more robust cost extra money, but making them to cheep affected reliability. Therefore, each part was made to be good enough, but not any better.

Same goes for the cooling system. Thermosyphon is probably not the best method for cooling an engine, but it worked good enough. A water pump would probably be a better design. However, a water pump would add to the cost of the car which goes against what Ford was trying to do with the Model T. I'm not an expert on Ford or the Model A, so I don't know what the reasons that Ford included a water pump on the Model A. The Model A produces twice the horse power of the T so that could be a factor. Maybe the price of the car was not as critical with the Model A so they felt it was worth the extra expense - who knows. But to say that the Model A having a water pump proves that theromsyphon doesn't work is just wrong.

Because things on the T were design to be "good enough but no better", one must be careful when making changes to the design. Making an improvement to one piece may have an adverse affect on other pieces. From my own personal experience, if you have a good radiator a water pump is not needed. From the experience of others who have done lots of tours, the consensus is that the cars with modifications tend to be the ones that have the problems. The most reliable are those which stuck with what Henry did. He knew what he was doing when he built that car.

Remember the times they lived in too. Unlike now, where we grew up with cars and engines and most of us were familiar with the basics... back then, internal combustion engines were brand new and a complete mystery to the average man and the first and only education he received as to how they worked and how they were serviced was by Ford. Heck. Even today many are ignorant about the basics of the internal combustion engine. My sister burnt up her first car in college in 1970 because she had no idea it needed oil and water and just last year, burnt up another car when she parked in tall, dry grass. Jim Patrick

Almost everyone has a thermosyphon system in their home,the water heater,cold water in the bottom displaces the hot water and pushes it out the top when the faucet is opened,the cold is heated and expand and goes to the top. A gallon of cool water weighs 8.33lb. and a gallon of 105 degree water will weigh about 2 lbs less, a Model T radiator is nothing more than a mobile water heater and we don't use the water. Rick

There you go, Rick. I dumped the thermosyphon water heater when it leaked a few years ago, because it's inefficient, and installed a tankless. The tankless uses 10 therms less NG every month, and is compact enough to mount on an outside wall, freeing up valuable kitchen space.

BTW, I don't recommend the tankless for everyone, but that's OT.

"A gallon of cool water weighs 8.33lb. and a gallon of 105 degree water will weigh about 2 lbs less.."

Where did you get that number, Rick? It sure doesn't fit on the above graph.

Ralph, 47 years in the plumbing ,heating and air industry.I was the western regional manager for Rinnai America and tankless or instant water are great if you have the gas capacity,in a great portion of the country you can't install them outside, you have less volume of water the higher the temp because of expansion,remember the arguments about boiling water freezing faster than plain temp water? it's true but look at the size of the ice of the two.Since i retired nine years ago i don't have access to all the charts and books,i gave them to the younger generation. Rick

Hmm, when we were young, my older brother told me about hot water freezing faster than cold water. We set two cans of water outside, and the cold one showed ice first. He accused me of swapping the cans around.

A neighbor gave me a Norjap tankless that had sprung a leak, and they wouldn't warranty it because we are on a well. I fixed it and used it a year. It was pure junk, anyhow. I spent my money on a Bosch, which is far better, and no well water restriction, they say.

You can actually use a thermosyphon system to circulate hot water around the house. You put the water heater low such as in basement or first floor, then run the hot water pipes through the attic and then down under the house and back to the heater. As the water heats it rises and as it cools it goes back to the heater. The various faucets are along the way and so you have hot water much quicker than if it is a one way system. This works well in Southern Ca because the attic gets quite hot so it even saves on the cost heating the water. I can't say how it would work in a cold climate where it might freeze in the attic.

If your T is in good condition, you shouldn't need a water pump. A pressurized system is well known to blow out freeze plugs, so be sure to keep a lot of nickels in your pocket and a couple gallons of water with you just in case. Norm

I don't have the exact calculations to figure it out, but steam occupies 1,600 times the volume that the same mass of water occupies in equilibrium.

I did a little experiment just to see how much of a weight difference there is between hot and cold water. I just had a bowl that hold maybe 2L and filled it with cold tap water, around 70F maybe less, and then again with hot tap water, I think 135F is what the heater is set on. I weighed them each separately and the results were 4.5lb for cold and 3lb for hot.

I can tell you that water expands quite a lot as a liquid, especially when it is superheated. When we fire our locomotive, we begin with a little over half a glass, boiler sight glass, at cold and by the time it begins to lift the needle on the pressure gauge the glass is almost slam full.

I'm not trying to be an expert or anything,I just work around hot water regularly and thought I'd share.

Hal, I consider any water that is heated beyond boiling point at atmospheric pressure. It's probably not the correct terminology to use, but that's just how I've always stated it. I know there's a big difference between a T and a boiler, I just threw that out for reference.

Thermosyphon systems don't work on density changes- which,by the way, are pretty small for water. They work on temperature differential- hot head versus "cold" radiator. Heat flows from hot to cold. Stand in front of your car on a chilly day. You feel the warmth of the radiator because heat is flowing to a cooler object- your body. Rob Roark

I disagree that thermosyphon is not based on water density. It is based on convection which is:

"Natural convection, or free convection, occurs due to temperature differences which affect the density, and thus relative buoyancy, of the fluid. Heavier (more dense) components will fall while lighter (less dense) components rise, leading to bulk fluid movement. Natural convection can only occur, therefore, in a gravitational field. A common example of natural convection is a pot of boiling water in which the hot and less-dense water on the bottom layer moves upwards in plumes, and the cool and more dense water near the top of the pot likewise sinks." (wikipedia - I know it's not the best source but it seems correct for this)

Thermosyphon most definitely works because of the change in density. Yes, there is a difference in temperature, but that is what causes the change in density. And just to split a few hairs, the only reason any fluid 'rises' because it is warmer is because it is being pushed up by the cooler fluid that is falling and taking it's place due to it being heavier. It is indeed gravity at work.

With regards to my experiment yesterday, there's a couple of variables that might have thrown it off a bit. The largest being the scale I used. Should have went back to test it again to verify the numbers. And as far as the sight glass goes, it's hard to tell exactly how much the water expands since the boiler is round. You have to remember too that this is being brought up to 180psi which would put the water temp at around 400F.

Robert, If someone took the time to download all the waterpump threads on the Forum going all the way back to the old forum up to present and organize each arguement chronologically, there would be enough for a book several hundred pages in length. Jim Patrick

Hot water natural circulation due to density and gravity and some of the molecules at 212F is not just a Model T phenom...it was the basis of hot water circulation long before someone had the thought of a 'pump' in a tech sense.

Now...the real issue is...does a water pump even pump????

I had one on the 25....for a while...never noticed any difference, in fact felt it actually was a smoother day when run without. I then looked inside the 'pump' and it is a curved 's' rotor that is nothing more than a 'paddle' with LOT'S of clearance to the housing! I turns maybe 3x as fast as the crank (just guessing at pulley differences!)

Even though I 'are' an engineer who got his college 'thermo' lessons from Lester J. Stradling reknown...and I have never played 'engineer' with the 'numbers' on a T...I have always suspected that pumps of the type I had on the 25 did NOTHING at high speed, maybe even cavitated, but at an idle sat there and simply 'helped' dump an ounce or two at a time into the 'top' as a rotating teaspoon which created a 'head' level difference for gravity to do its thing.

Just an old guys thoughts...a guy who should know better and think it through...but also a guy who now has a water pump hanging on the side of his garage wall

Since many of them are so poorly designed and may not pump water at all, maybe they could be renamed "belt-driven conversation pieces" and then the purists wouldn't be so offended by the owners having added them.

Actually it is possible to get the old pumps to pump. When I got mine it was in pretty bad shape. The shaft was worn, the impeller looked like the stirrer in a milkshake machine, the packing was gone and so on. I got some sheet copper and made an impeller by soldering bits to the old vanes and then attached a cage to the new vanes.

I took the advise of the forum and took my waterpump off the first day my T came home. I have dealt with leaking Model A water pumps, cutting sponges to fit around the shaft and putting a leater boot over the whole mess. My dad showed me the level to fill my radiator and to not overfill it. I did 6 parades this last summer, two were in 100 degree weather! I have yet to add any more water, or even get to see any steam!! My waterpump will continue to hang on a nail on a wall for display.

I don't use a water pump on my cars (stock or Fronty speedster) and haven't had any issues letting nature handle the circulation. I do use a fan most of the time but found it isn't needed as long as I don't sit in traffic too long.

You got it, Bud. . Probably every old waterpump out there has a rust pitted shaft that won't seal, and people act as if they have always been that way, and are non-repairable. I bought a stainless shaft, bushings and seals from www.McMaster.com about ten years ago, and my Henry pump hasn't leaked since.

------------ Wiki:

Perhaps the best example of purely mechanical technology in widespread use today is the internal combustion engine cooling thermostat. These are used to maintain the core temperature of the engine at its optimum operating temperature by regulating the flow of coolant to an external heat sink, usually an air cooled radiator. Also, research in the 1920's showed that cylinder wear was aggravated by condensation of fuel when it contacted a cool cylinder wall which removed the oil film, and the development of the automatic thermostat in the 1930's provided a solution to this problem by ensuring fast engine warm-up[3].

This type of thermostat operates mechanically. It makes use of a wax pellet inside a sealed chamber. The wax is solid at low temperatures but as the engine heats up the wax melts and expands. The sealed chamber has an expansion provision that operates a rod which opens a valve when the operating temperature is exceeded. The operating temperature is fixed, but is determined by the specific composition of the wax, so thermostats of this type are available to maintain different temperatures, typically in the range of 70 to 90°C (160 to 200°F). Modern engines run hot, that is, over 80°C (180°F), in order to run more efficiently and to reduce the emission of pollutants. Most thermostats have a small bypass hole to vent any gas that might get into the system, e.g., air introduced during coolant replacement, which also allows a small flow of coolant past the thermostat when it is closed. This bypass flow ensures that the thermostat experiences the temperature change in the coolant as the engine heats up; without it a stagnant region of coolant around the thermostat could shield it from temperature changes in the coolant adjacent to the combustion chambers and cylinder bores.

While the thermostat is closed, there is no flow of coolant in the loop allowing the combustion chambers to warm up rapidly. The thermostat stays closed until the coolant temperature reaches the nominal thermostat opening temperature. The thermostat then progressively opens as the coolant temperature increases to the optimum operating temperature, increasing the coolant flow to the radiator. Once the optimum operating temperature is reached, the thermostat progressively increases or decreases its opening in response to temperature changes, dynamically balancing the coolant recirculation flow and coolant flow to the radiator to maintain the engine temperature in the optimum range as engine heat output, vehicle speed, and outside ambient temperature change. Under normal operating conditions the thermostat is open to about half of its stroke travel, so that it can open further or reduce its opening to react to changes in operating conditions. A correctly designed thermostat will never be fully open or fully closed while the engine is operating normally, or overheating or overcooling would occur. For instance,

If more cooling is required, e.g., in response to an increase in engine heat output which causes the coolant temperature to rise, the thermostat will increase its opening to allow more coolant to flow through the radiator and increase engine cooling. If the thermostat were already fully open, then it would not be able to increase the flow of coolant to the radiator, hence there would be no more cooling capacity available, and the increase in heat output by the engine would result in overheating. If less cooling is required, e.g., in response to decrease in ambient temperature which causes the coolant temperature to fall, the thermostat will decrease its opening to restrict the coolant flow through the radiator and reduce engine cooling. If the thermostat were already fully closed, then it would not be able to reduce cooling in response to the fall in coolant temperature, and the engine temperature would fall below the optimum operating range. -----------